<template>
  <div class="slider" ref="slider">
    <div class="slider-group" ref="sliderGroup">
      <slot>
      </slot>
    </div>
    <div class="dots">
      <span class="dot" :class="{active: currentPageIndex === index}" v-for="(item, index) in dots"></span>
    </div>
  </div>
</template>

<script type="text/ecmascript-6">
import BScroll from 'better-scroll'
import {addClass} from 'common/js/dom'

export default {
  props: {
    loop: {
      type: Boolean,
      default: true
    },
    autoPlay: {
      type: Boolean,
      default: true
    },
    interval: {
      type: Number,
      default: 4000
    }
  },
  data () {
    return {
      dots: [],
      currentPageIndex: 0
    }
  },
  mounted () {
    setTimeout(() => {
      this._setSliderWidth()
      this._initDots()
      this._initSlider()

      // 自动轮播
      if (this.autoPlay) {
        this._play()
      }
    }, 20)

    // 监听window.resize事件，也就是视口的大小是否改变
    window.addEventListener('resize', () => {
      // slider还没有初始化的时
      if (!this.slider) {
        return
      }
      // 传入true,是为了不让宽度计算两遍
      this._setSliderWidth(true)
      // 当宽度发生变化，要重新计算Beterscroll
      this.slider.refresh()
    })
  },
  methods: {
    // 手动计算并设置这个宽度，整个列表有多少个元素
    _setSliderWidth (isResize) {
      this.children = this.$refs.sliderGroup.children
      console.log(this.children)
      let width = 0
      let sliderWidth = this.$refs.slider.clientWidth
      for (let i = 0; i < this.children.length; i++) {
        let child = this.children[i]
        console.log(child)
        addClass(child, 'slider-item')

        child.style.width = sliderWidth + 'px'
        width += sliderWidth
      }

        console.log(width)
        // 没看懂为啥要判断是否是改变过视口大小
        if (this.loop && !isResize) {
          console.log("2*width")
          width += 2 * sliderWidth
        }
        this.$refs.sliderGroup.style.width = width + 'px'
    },
    _initSlider () {
      this.slider = new BScroll(this.$refs.slider, {
        // 横向滚动
        scrollX: true,
        // 不允许纵向滚动
        scrollY: false,
        // 惯性不允许
        momentum: false,
        snap: true,
        // 循环
        snapLoop: this.loop,
        snapThreshold: 0.3,
        snapSpeed: 400
      })

      this.slider.on('scrollEnd', () => {
        let pageIndex = this.slider.getCurrentPage().pageX
        console.log(pageIndex)
        if (this.loop) {
          console.log("has loop")
          pageIndex -= 1
          console.log(pageIndex)
        }
        this.currentPageIndex = pageIndex

        if (this.autoPlay) {
          console.log("has autoPlay")
          this._play()
        }
      })

      // 将计时器格式化，防止手动往后面滑动时，出现紊乱
      this.slider.on('beforeScrollStart', () => {
        if (this.autoPlay) {
          clearTimeout(this.timer)
        }
      })
    },
    _initDots () {
      this.dots = new Array(this.children.length)
      console.log(this.dots)
    },
    _play () {
      let pageIndex = this.currentPageIndex + 1
      if (this.loop) {
        pageIndex += 1
      }
      this.timer = setTimeout(() => {
        this.slider.goToPage(pageIndex, 0, 400)
        console.log("goto pageIndex")
      }, this.interval)
    }
  }
}
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
@import "~common/stylus/variable"

.slider
  min-height: 1px
  .slider-group
    position: relative
    overflow: hidden
    white-space: nowrap
    .slider-item
      float: left
      box-sizing: border-box
      overflow: hidden
      text-align: center
      a
        display: block
        width: 100%
        overflow: hidden
        text-decoration: none
      img
        display: block
        width: 100%
  .dots
    position: absolute
    right: 0
    left: 0
    bottom: 12px
    text-align: center
    font-size: 0
    .dot
      display: inline-block
      margin: 0 4px
      width: 8px
      height: 8px
      border-radius: 50%
      background: $color-text-l
      &.active
        width: 20px
        border-radius: 5px
        background: $color-text-ll
</style>
